Active heating technologies can be applied to subsea pipelines to tackle challenging reservoir flow assurance constraints that could take place during production shut down and normal subsea field operation (i.e. hydrate, gelling, wax and/or high oil viscosity). Implementation of active heating to subsea pipelines enables i) field architecture simplification and ii) long subsea tie-backs. The Electrically Trace Heated Pipe-in-Pipe (ETH-PIP) is a standard reelable PIP system enhanced with up to 4-off trace heating cables and 2-off fiber optic (FO) cables, for temperature monitoring purposes, spiraled against the inner pipe and covered by high thermal performance insulation allowing a high thermal system efficiency. The high thermal efficiency combined with a primarily resistive electrical system makes the ETH-PIP the most energy efficient active heating technology. Long power heating/transmission line can be described by the fundamental parameters resistance/inductance of conductor and capacitance/conductance of insulation. The analysis of the overall heating system can be assessed using three alternative models: i) the most simple and compact RL model where only total resistance and total inductance of line is included, ii) more advanced RLC model where the total capacitance of insulation is additionally included and iii) the most advanced distributed RLGC (resistance, inductance, conductance, capacitance) model where total length of line is modelled as a chain of shorter RLGC segment lengths. The accuracy of each model depends on multiple aspects such as: heating/transmission line parameters, required heating power, total length of line, mode of operation, environmental conditions, etc. The proper and careful selection of the appropriate model to ensure effective computation and results accuracy is paramount. The paper includes the detailed description of each heating/transmission line model. Additionally, each model is illustrated on a set of theoretical examples.
Subsea oil and gas production can utilize a number of technical solutions to ensure efficient and cost- effective operation. There are two main technologies applied to address flow assurance challenges in case of particularly long tieback reservoirs: subsea active heating and subsea boosting. The production from distant reservoirs with challenging flow assurance conditions may require application of both mentioned systems. In such case, one challenge relies on the selection of a power supply infrastructure for both systems, considering all possible optimization aspects. In the conventional approach, the implementation of both systems is realized independently. Subsea active heating system and subsea boosting system are supplied and monitored from topside by the separate power strings. However, the development of subsea technologies allows to review the approach and consider integration of both systems, enabling reduction of topside infrastructure for general cost savings. The purpose of this article is to present the integrated system composed of Electrically Trace Heated Pipe in Pipe (ETH-PIP) and subsea boosting pumps where Variable Speed Drive (VSD) is required. The role of both system is shortly presented. Next, a proposal of an integrated power system for subsea heating and boosting is illustrated and discussed on a case study example. The analysed field layout is characterized by a long tie-back to a production facility where both subsea boosting and active heating systems are necessary operating in the relevant power modes. The results of analysis allow to conclude that the presented solution can be valuable alternative to traditional approach of complex subsea system topologies.
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